In certain types of computing systems that include a central processing unit (CPU) and a host bridge or what is known as a “Northbridge,” such devices are connected by an interface using a particular protocol in order for the CPU and Northbridge to communicate. One such protocol known in the art is HyperTransport™, which provides a high speed, point-to-point link for interconnecting integrated circuits within a computing system. Typically, however, Northbridge circuits communicate with other devices in the system, such as input-output bridges (e.g., a “Southbridge”) according to different protocols, including PCI Express. Different protocols may use different packet formats and different commands in the packets. Accordingly, when a CPU is trying to communicate with a Southbridge via the Northbridge and the CPU communicates with the Northbridge via HyperTransport™ protocol and the Northbridge, in turn, communicates with the Southbridge via PCI Express protocol, not all message types or packet formats are easily passed through the Northbridge to communicate the commands in requests (e.g. packets) from the CPU to the South bridge.
Particularly, certain protocols, such as HyperTransport™, utilize two types of memory write commands in memory write requests. In the example of HyperTransport™, in particular, it is known to utilize both “posted” and “non-posted” memory write commands. Posted commands are simply sent from a CPU to a Southbridge via a Northbridge, for example, without the need for a return acknowledgment. On the other hand, non-posted commands require that the receiving device issue an acknowledgement that the memory write request with the non-posted command has been made. PCI Express, on the other hand, only utilizes the concept of the equivalent of posted memory write requests of HyperTransport™ protocol. This difference becomes particularly problematic with Southbridges incorporating an internal bridge to a low pin count (LPC) interface, which is an interface that may connect to devices having both slave and/or master interfaces and also converts to LPC protocols.
The LPC protocol, however, does not account for or allow memory write requests to be retried with the master interfaces. In particular, once a bus master is granted control of the LPC interface, it will not release the interface before a transaction or write request is successfully completed. When the Southbridge grants an external LPC interface master control of the interface, the Southbridge is unable to service transactions, namely memory write requests, from the CPU that are targeting a particular device connected to the LPC interface. Thus, when the LPC interface master is performing direct memory access reads from a main system memory, it is possible that the CPU may also be performing “posted” memory write requests to another device connected to the LPC interface. However, because the LPC interface master “owns” the LPC interface at the time, the posted memory write requests cannot be completed. This situation is further complicated in that known ordering rules for such interfaces prevent read response data from passing the posted memory write requests, which may result in deadlock of the Southbridge as well as the entire computing system.
It is noted that the following documents are known in the art concerning HyperTransport™ technology and PCI and their functioning. The following documents are incorporated herein by reference:    1) “HyperTransport™ I/O Link Specification, Revision 1.05c”; Document #HTC2002104-0005-0005; Aug. 5, 2003; HyperTransport Technology Consortium.    2) “HyperTransport™ I/O Link Errata, Revision 1.05b”; Document #HTC200335-0024-0003; Apr. 2, 2003, HyperTransport Technology Consortium.    3) “Advanced Configuration and Power Interface Specification, Revision 2.0b;” Oct. 11, 2002; Compaq Computer Corporation, Intel Corporation, Microsoft Corporation, Phoenix Technologies Ltd., and Toshiba Corporation.    4) “AMD-8151™ HyperTransport™ AGP3.0 Graphics Tunnel Data Sheet;” 24888 Rev 3.03-Jul. 12, 2004; Advanced Micro Devices, Inc.    5) “Clock Generator Specification for AMD64 Processors;” Publication #24707 Revision: 3.08; September 2003; Advanced Micro Devices, Inc.    6) “HyperTransport™ Technology I/O Link—A High-Bandwidth I/O Architecture;” Jul. 20, 2001; Advanced Micro Devices, Inc.